In offshore drilling and hydrocarbon recovery there are risks that materials released into the water surrounding the wellhead or the drilling and/or production platform may reach levels at which marine life in the vicinity is endangered. Discharges may be operational or accidental. Thus examples of operational discharges include produced water during the production stage and drilling fluids and cuttings during the drilling stage. Examples of accidental discharges include hydrocarbons, hydraulic fluids, drilling fluids, cuttings and other chemicals. It is important that such discharges do not cause unacceptable water contamination or other environmental effects and so, when unacceptable discharges occur, it is important for the well operator to take action to reduce or stop contaminant release.
Such actions may include shutting down drilling operations, stopping hydrocarbon recovery, replacing or repairing equipment, and so on, all of which are expensive. It is therefore important for the well operator to be able to determine not only that contamination has occurred but also the source, nature and severity of the contamination: thus for example if contamination is as a result of leakage from passing shipping, corrective action by the well operator would be ineffective, and if contamination is below threshold values for severity then corrective action may as yet not be required.
Monitoring of contamination of water masses is well-known; however the prior art is mostly concerned with downstream monitoring of flowing fresh water, monitoring of effluent discharges from factories, and general monitoring of offshore waters. Little attention has been given to the effective monitoring of seawater surrounding offshore hydrocarbon wells in order to detect contamination by the well rather than contamination in the vicinity of the well. There is thus a need for monitoring systems useful in this regard.